Letrozole

Letrozole, available under the brand name Femara, is a kind of hormonal therapy called an aromatase inhibitor. It is used to treat hormone receptor-positive breast cancer, or to reduce its risk of recurrence (cancer coming back).

Like the other aromatase inhibitors, letrozole works by blocking the activity of an enzyme called aromatase. Aromatase changes other hormones into estrogen. Blocking aromatase lowers estrogen levels in the body. This can slow or stop the growth of hormone receptor-positive breast cancer.

Other aromatase inhibitors include anastrozole (Arimidex) and exemestane (Aromasin).

Who gets letrozole?

Letrozole is FDA-approved to treat postmenopausal women with hormone receptor-positive breast cancer. It can be used:

• To lower the risk of recurrence for early-stage breast cancer. It might be the first hormonal therapy given, or it might be used after tamoxifen.
• To slow or stop the growth of metastatic breast cancer.

Letrozole can also be used to treat hormone receptor-positive breast cancer in pre- and perimenopausal women, as well as men. They must also take a medicine called a gonadotropin-releasing hormone agonist (GnRH agonist).

• In pre- and perimenopausal women, GnRH agonists suppress ovarian function, putting the body into temporary menopause. This greatly reduces estrogen levels.
• In men, GnRH agonists lower production of the male hormone testosterone. Normally, some testosterone is converted into estrogen. Reducing testosterone lowers the amount of estrogen produced.

Some pre- and perimenopausal women decide to have their ovaries removed (oophorectomy) instead of taking ovarian suppression medicines. Still, it is important to know that oophorectomy causes early menopause that is not reversible. Many women choose GnRH agonists instead. Talk with your care team about what’s right for you.

How is letrozole given?

Letrozole is a 2.5 milligram pill taken every day.

Side effects and things to remember

If you have cirrhosis (scarring or hardening of the liver) or other serious problems with liver function, your doctor may recommend taking letrozole every other day. Your doctor also may order blood tests to check your liver function before and during treatment. You can discuss your medical history to figure out what makes sense for you.

In addition, letrozole can cause:

• Bone loss. Aromatase inhibitors such as letrozole can cause bones to become thinner. Your doctor may recommend tests to check your bone density before and during treatment. When bone loss happens, it can lead to a condition called osteoporosis, which increases the risk of fracture. Still, there are ways to reduce the risk. Learn more about bone health.
• Increases in cholesterol levels. Your doctor might recommend checking your cholesterol levels before and during treatment.
• Fatigue, sleepiness, and dizziness.

Letrozole can cause many of the same side effects as other aromatase inhibitors, including:

• Menopausal symptoms including hot flashes; genitourinary syndrome of menopause, such as vaginal dryness and irritation; and loss of interest in sex
• Stiffness and joint and bone pain
• High blood pressure
• Nausea and vomiting
• Weakness
• Headache
• Loss of appetite
• Weight gain
• Mood changes
• Constipation or diarrhea
• Dry skin
• Hair thinning